Method and apparatus for dry forming webs of pulp from vegetable fibrous material

ABSTRACT

THIN INVENTION RELATES TO A METHOD AND AN APPARATUS FOR CONTINUOUS DRY-FORMING A WEB OR BAT OF PULP FROM VEGETABLE FIBROUS MATERIAL ON AN ENDLESS WIRE SCREEN BY INTRODUNG INTO A FORMING CHAMBER OPENING TOWARDS SAID WIRE SCREEN A DISPERSION OF FIBERS IN A GAS AND SIMULTANEOUSLY CREATING ON THE REAR SIDE OF SAID WIRE SCREEN OPPOSITE TO SAID FORMING CHAMBER SO MUCH REDUCED PRESSURE THAT MORE GAS IS SUCKED THROUGH THE WIRE SCREEN THAN IS APPLIED WITH THE VEHICLE GAS IN THE DISPERSION OF FIBERS   IN GAS, THE ADDITIONAL GAS BEING INTRODUCED BETWEEN SAID WIRE SCREEN AND THE LOWERMOST PORTION OF THE FORMING CHAMBER, AND BY RECIRCULATING THE WITHDRAWN GAS THROUGH A CONDUIT SYSTEM TO THE FEED SIDE OF THE FORMING CHAMBER TOGETHER WITH NEW FIBROUS MATERIAL. THE ADDITIONAL GAS IS WITHDRAWN FROM THE CONDIUT SYSTEM TO AVOID INTRODUCTION OF ATMOSPHERIC AIR.

Oct. 12, 1971 R. B. REINHALL. ETAL 3,611,508 METHOD AND APPARATUS FOR DRY FORMING WEBS 0F PULP I FROM VEGETABLE FIBROUS MATERIAL Filed Feb. 27, v1969 4. Sheets-Sheet 1 FIG. 4

HALL I enters: ROLF BERTIL REI nv and KARL NICOLA'US DERQUIST Attorney: ERIC Y MUNSON Oct. 12, 1971 R. B. REINHALL I' L 3,511,508

METHOD AND APPARATUS FOR DRY FORMING WEBS OF PULP FROM VEGETABLE FIBROUS MATERIAL Filed Feb. 27, 1969 4 Sheets-Sheet 3 FIG. 2

I nvcn tors ROLF BLZR'IIL PJ'. I HHALL and KARI. NICOLAUS CEDI'LPQUIILT Attorney: ERIC Y. MUNSON Oct. 12 1971 RI 'BfREINHALL EI'AL 3,611,508

METHOD AND APPARATUS FOR DRY FORMING WEBS OF' PULP FROM VEGETABLE FIBROUS MATERIAL Filed Feb. 27, 1969 4 Sheets-Sheet 8 FIG. 3

lmuuwq Inventors: ROLF BERTIL REINHALL and KARL NICOLAUS CEDHRQUIS'I Attorney: ERIC Y. MUNSON Oct. 12, 1971 R. B. REINHALL ETA!- 3,511,503

METHOD AND APPARATUS FOR DRY FORMING WEBS OF PULP FROM VEGETABLE FIBROUS MATERIAL Filed Feb. 27, 1969 4 Sheets-Sheet FIG. 4

Inventors: ROLF BERTIL REINHALL and KARL NICQLAUS CEDERQUIST Attorney: ERIC Y. MUNSON United States Patent US. Cl. 19156.3 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method and an apparatus for continuous dry-forming a web or bat of pulp from vegetable fibrous material on an endless wire screen by introducing into a forming chamber opening towards said wire screen a dispersion of fibers in a gas and simultaneously creating on the rear side of said wire screen opposite to said forming chamber so much reduced pressure that more gas is sucked through the wire screen than is applied with the vehicular gas in the dispersion of fibers in gas, the additional gas being introduced between said wire screen and the lowermost portion of the forming chamber, and by recirculating the withdrawn gas through a conduit system to the feed side of the forming chamber together with new fibrous material. The additional gas is withdrawn from the conduit system to avoid introduction of atmospheric air.

This invention relates to a method and an apparatus for dry forming a web of pulp from fibrous material.

More particularly this invention relates to a method and an apparatus for continuous dry-forming a web or bat of pulp from vegetable fibrous material on an endless wire screen by introducing into a forming chamber opening towards said wire screen a dispersion of fibers in a gas and simultaneously creating on the rear side of said wire screen opposite to said forming chamber so much reduced pressure that more gas is sucked through the wire screen than is supplied with the vehicular gas in the dispersion of fibers in gas, the additional gas being introduced between said wire screen and the lowermost portion of the forming chamber, and by returning the content of dust particles in the withdrawn gas through a conduit system to the feed side of the forming chamber together with new fibrous material.

To exemplify the prior art reference is made to the US. Pat. No. 2,3 89,024 according to which the additional gas is constituted by air sucked into the forming chamber through openings formed therein. Entrained solid particles are separated off in a box below the wire screen and returned by a conveyor to the feed side. Another example is the US. Pat. No. 2,940,134, according to which more air is sucked through the wire screen than is supplied to the forming chamber together with the fibrous material. The additional air is added in the zone where the dry forming is effected. The air sucked through the wire screen is blown into a cyclone, Where a separation is effected into air free from fibers which is blown out into the surrounding atmosphere and air relatively rich in fibers which is returned to the feed stream to which also a predetermined quantity of air from the free atmosphere is added in connection with the feeding of the fibrous material into the forming chamber.

The fibrous material is preferably produced by defibration of wood, straw, bagasse etc. in an atmosphere of saturated steam at a temperature between 140 and 240 Patented Oct. 12, 1971 C. and a corresponding steam pressure, said defibration preferably being effected according the so-called Defibrator method. After the defibration, the fibrous material which usually has a relative high moisture content, such as 40 to 60 percent, must be dehydrated to a moisture content of about 5 to 25 percent to be suited for the subsequent dry forming treatment. This pretreatment thus does not affect, in itself, the present invention.

One main object of the invention is to provide an improvement of methods hitherto applied for the forming the pulp web on the endless wire screen so as to cause the gas required to circulate in various circuits without but to an insignificant degree communicating with the surrounding atmosphere or to be intermixed with air from said atmosphere. The circulating gas streams contain solid dust to a more or less high degree, and thus a further object of the invention is to avoid that this dust is distributed over the surroundings which thereby could be contaminated with dust particles in an annoying manner.

A particularly important advantage attained with the closed gas circulation is that the risk of fire can be eliminated almost entirely by introducing into the circulation system gases having a low oxygen content such as flue gases. As the feed into, and distribution within, the forming chamber is effected with a practically enclosed qauntity of gas, such gas poor in oxygen is prevented from escaping into the surrounding.

According to one main feature of the invention, new fibrous material is introduced into the said conduit system through a sluice device and entrained by the vehicular gas flowing within said system without direct admixture of air from the surrounding atmosphere, said vehicular gas besides of a stream of gas withdrawn from the rear side of the wire screen including a quantity of gas corresponding to a branch stream of gas circulating within a circuit provided beside of said forming chamber, a second branch stream originating from the withdrawn through said wire screen being used as the additional gas.

Further objects and advantages of the invention will become apparent from the following description, considered in connection with the accompanying drawings, which form part of the specification, and in which:

FIG. 1 is a diagrammatic view of an apparatus intended for carrying out the method of the invention,

FIG. 2 is an enlarged partial view of this apparatus,

FIG. 3 shows a modified embodiment of an apparatus according to the invention,

FIG. 4 is a diagrammatic view of an apparatus for drying fibrous material by means of flue gases which at least in part are intended to become included in the gaseous fluid in the fiber web forming apparatus.

In the various figures equivalent parts have been denoted by the same reference numerals.

Referring now to the embodiment shown in FIGS. 1 and 2, reference numeral 10 denotes a forming chamber which suitably widens in downward direction, reference numeral 12 denoting a suction box located straight below said chamber. An endless wire screen 14 runs about guide rolls 16, of which two are indicated in the figures. The upper track of the wire screen 14 moves in the direction of the arrow 18 through the interspace between the forming chamber 10 and the suction box 12. The forming chamber 10 is provided with sealing means 20, 2.2. preferably of the labyrinth type at the places where the endless wire screen 14 enters between, and leaves, respectively, the interspace between the chamber and the suction box. The labyrinth type sealing means may be provided with flexible and resilient members 24 (FIG. 2) devised to seal against the wire screen 14 proper and the web of pulp deposited on the screen at the outlet side of the forming chamber. 'It is thereby ensured that the suction of air from the surrounding atmosphere into the forming chamber is reduced to a minimum value.

In case that a gas other than air, such as flue gas, is used in the apparatus, a separate conduit 26 can be connected to sockets 27 for supply of such gas to the interspace 25 formed by the labyrinth sealing means. This alternative shall be described below in more detail.

A conduit 28 from the suction box 12 is connected to the suction side of a blower or fan 30. From the pressure side of said blower, a conduit 32 (FIG. 1) extends to a cyclone 34 into which said conduit opens tangentially in a manner known per se. The gas, such as air, entering the cyclone 34 contains an appreciable quantity of fiber dust. A separation is effected in said cyclone so that gas practically free from dust passes through a central conduit 36 into a pressure equalization chamber 38. The dust separated Oil falls down within the cyclone 34 and is ted through a sluice device 40 opening towards a conveyor 42 onto which new fibrous material is fed through an opening 44. The fibrous material is then fed past a measuring device 46 and through a second sluice device 48 onto a conveyor 50.

From the conveyor 50, the fibrous material is introduced into a conduit 52 connected to the suction side of a blower or fan 54. The pressure side of said blower is through a conduit 56 in connection with a cyclone 58, which suitably is located at the top of, and communicates with, the forming chamber 10. The conduit 56 opens tangentially into the cyclone 58, a conduit 60 leaving said cyclone from the central section thereof being connected to the pressure equalization chamber 38. In the cyclone 58, such separation is effected that a branch gas stream practically free from dust is conducted through the conduit 60 into the equalization chamber 38. The major part of the gas together with the fibrous material is fed downwards from the cyclone 58 into the forming chamber 10.

The main portion of the return gas stream from the cyclone 34 is returned from the equalization chamber 38 through the conduit 36 into the conduit 52 and therethrough to the suction side of the blower 54 where said gas stream is intermixed with the fibrous material from the conveyor 50. This gas stream is augmented in the conduit 52 by the gas stream returned through the conduit 60 so as to collect a suflicient quantity of vehicular gas to ensure a satisfying conveyance of the fibrous 'material through the conduit 56 to the cyclone 58.

A portion of the gas stream purified by separation from dust in the cyclone 34 and conducted through the conduit 36 into the pressure equalization chamber 38 is fed through a conduit 62 to a box or chamber 64 connected with a channel 66 opening into the forming chamber most suitably at the side thereof where the endless wire screen 14 with the web or layer of fibers resting thereon leaves said chamber. This branch stream of gas which also is termed as additional gas, is thus introduced through the channel or gap 66 into the vehicular gas for the fibrous material originating from the cyclone 58 and is withdrawn or sucked olf together with said vehicular gas through the wire screen into the suction box 12 by means of the blower fan 30 while a layer or web of fibers is deposited on the screen 14. In collaboration with the sealing means 20, 22 the additional gas results in that penetration of air from the outer atmosphere into the system is reduced to a minimum. The downwards directed gas stream from the cyclone 58 together with the additional gas from the channel 66 continues through the conduit 32.. In the cyclone 34 dust entrained by the gas stream is separated off, as already mentioned, and the purified gas stream is caused to enter the equalization chamber 38. In this chamber, a branching is effected in such a manner that a branch stream corresponding to the additional gas is passed through the conduit 62, the box 64 and the channel 66 into the lowermost portion of the forming chamber 10. The main part of the gas flowing through the conduit 36 into the equalization chamber 38 is introduced into the conduit 52 to constitute vehicular gas for new fibrous material. This vehicular gas in addition includes the return gas stream from the cyclone 58 through the conduit 60. In the embodiment now described the vehicular gas is practically entirely composed of the quantity of gas carrying the fibrous material downwards into the forming chamber 10 and the branch stream which upon purification from fibrous material leaves the cyclone 58 through the conduit 60.

The pressure equalization chamber 38 with its outlet 39 to the surrounding atmosphere has for its object to provide for the correct pressure distribution in the conduit systems so that gas will escape or enter through the opening 39 from or to the equalization chamber to the extent as the pressure in said chamber exceeds or is below a predetermined value.'Due to the fact that the additional gas supplied to the lower portion of the forming chamber and the increase of the gas content of the dispersion of fibers and gas in the conduits 52, 56 is eliected by means of air circulating in closed circuits, the exchange of air with the surroundings will become very low and can thus substantially be limited to the relatively insignificant unavoidable leakage through the sealing means 20, 22. To this favorable result contributes also the feature that the sluice devices 40 and 48 permit conveyance of solid stuff and fibrous material, respectively, into and out from the conduit systems without atmospheric air following in an extent worth mentioning.

The embodiment presented in FIG. 3 differs from the preceding one therein that the gas stream leaving the suction box 12 is conducted through a conduit 68 directly into the cyclone 58 located on the top of the forming chamber. This gas stream is simultaneously intermixed with new fiber material supplied through the inlet 44- and through the sluice devices 40 and 48, respectively, and the measuring device 46 introduced into the conduit 68 by the conveyor 50. The branch gas stream made free from fibrous material in the cyclone 58 passes through the conduit 60 into the pressure equalization chamber 38 and is sucked off by a blower fan 70 and conducted through a conduit 71 into the cyclone 34. In the same manner as in the preceding embodiment, separated dust falls down within said cyclone whereas the central conduit 36 is split up into two branches of which the one, denoted 72, opens into the conduit 68 immediately ahead of the place where the conveyor 50 delivers new fibrous material to said conduit. Hereby, the dispersion of fibers in gas is still improved by further gas so that the fibrous material can be carried to the cyclone 58 without meeting any obstacles. The other branch conduit 74 from the conduit 36 delivers a quantity of gas approximately corresponding to the additional gas entering the equalization chamber 38 which gas thereupon flows through the conduit 62, the box 64 and the channel 66 to the forming chamber 10.

The invention is extremely well suited to be applied to apparatus in which instead of air a gas poor in oxygen is used in one or several of the various circulation circuits. If the circulating gas is constituted by air, the risk of dust explosion increases in the same degree as the water content of the fibrous material decreases. If, however, the air is replaced by inert gases, which contain 10 percent of oxygen at the utmost, the explosion risk will practically become eliminated, as experience has shown. An inert gas containing between 5 and 10 percent of molecular oxygen can be produced in the shape of flue gas, which upon liberation from moisture excess, dust, primarily soot particles, and acid constituents can be used to advantage in the forming process. Such flue gases can be obtained from the dehydrator apparatus in which the defibrated fibrous material is dehydrated before becoming subjected to the treatment described hereinbefore. The dehydration can thus be effected with circulating hot furnace gases consisting of a mixture of flue gases and steam. Flue gases low content of oxygen can be introduced through the conduit 26, for example, into the labyrinth sealing means 20, 22 or through a conduit 120 into the pressure equalization chamber 38. Flue gas may, if desired, also be introduced directly into one or several of the circulation conduits as is indicated at 122 in FIGS. 1 and 3. The supply of flue gas is adjusted so that the content of oxygen in the conduit circuits will be sufficiently low to ensure that no danger of explosion will come to existence. At the same time, it is made sure by the construction of the forming apparatus according to the invention that the escape of flue gas to the surroundings will become insignificant.

formed in this way can be cooled down in advance so much as to cause a substantial part of the steam to precipitate by condensation before the gas is supplied to the circulation circuits according to the invention.

FIG. 4 shows a dehydrator apparatus for the fibrous 5 material finely divided in a grinding device, preferably a defibrator. This apparatus comprises a furnace 76 which is fired, for example, with oil in a burner 78 together with atmospheric air introduced into the furnace. The hot flue gas is mixed with returned gas and steam from a conduit 80 so that the gas temperature after the intermixing does not exceed 400 C. The gas mixture obtained in this way in the furnace is sucked by ablower fan 82 through a conduit 84, a cyclone 86, a conduit 88, and a mixing chamber 90 to a drier or dehydrator 92 indicated diagrammatically in FIG. 4. At the same time, wet fiber pulp together with steam from a defibrator 94 is blown into the chamber 90. A strong re-mixing and disintegration with subsequent evaporation is efiected by the blower fan 82 and the final dehydration is effected in the dehydrator 92. The dry fibers are conveyed through a conduit 96 to a cyclone 98 by means of the flue gas stream, under which operation they are separated off and conveyed through a cooling device 100 and a conveyor 102 to the inlet opening of the forming station or chamber. The mixture of gas and steam returns to the furnace 78 through the conduit 80. Part of the mixture corresponding to the quantity of newly formed gas and steam is conducted through a pipe 104 to a scrubber 106 where steam is precipitated by condensation and the gas purified by separation from dust and acid constituents. The scrubber has for this purpose spraying member 108 supplied with cooling water through a pipe 110. A pipe 112 forms together with the pipe 104 a heat exchanger 114 in which the purified and dehydrated flue gas flowing in the pipe 112 is subjected to some heating. The cooling water leaves the scrubber 106 through a pipe 116 and is made free from solid particles in a filter 118.

The flue gas streaming in the pipe 112 and which has a Instead of cyclones, other dust traps such as filters, for

If desired, a filter for trapping the small quantities of dust which possibly could escape from the pressure equalization chamber 38, may be provided in the outlet 39 from said chamber.

While several more or less specific embodiments of the invention have been shown and described, it is to be understood that this is for purpose of illustration only and that the invention is not to be limited thereby, but its scope is to be determined 'by the appended claims.

What we claim is: 1. A method of continuously dry forming a web of pulp from vegetable fibrous material comprising:

(a) conducting a first gas stream having fibrous material entrained therein through a screen to form said web thereon,

(b) recirculating a major part of said first gas stream along a path from one side of said screen to the other side thereof to pass again through said screen,

(c) entraining additional fibrous material in said first gas stream at a first point along said path to form a gas-fibrous material mixture,

((1) separating a part of said gas from said first gas stream at a second point in said path downstream from said first point and upstream from said screen to form a second gas stream,

(e) recycling said second separated gas stream and introducing it into said first gas stream at a third point in said path upstream from said first point along the path where said fibrous material is entrained to supplement said first gas stream, and

(f) withdrawing a third gas stream from said second gas stream and supplying said third gas stream as additional gas to said first gas stream having fibrous material entrained therein as the first gas stream passes through said screen,

(g) whereby the introduction of atmospheric air is reduced to a minimum.

2. A method according to claim 1 wherein said third gas stream is withdrawn from said second gas stream, entrained fibrous material carried over from said first gas stream being removed from said second gas stream be fore the withdrawal of said third gas stream.

3. A method according to claim 1 wherein said third gas stream is subjected to pressure equalization by exposing it to the atmosphere before adding said third gas stream to said first gas stream as the first gas stream passes through said screen.

4. A method according to claim 1 wherein said second gas stream is subjected to pressure equalization 'by exposing it to the atmosphere before introducing said second gas stream into said first gas stream.

5. An apparatus for continuously forming a web of pulp from vegetable fibrous material comprising:

(a) means defining a forming chamber having an opening in one side thereof,

(b) means defining a suction box having an opening in one side thereof spaced from said opening in said forming chamber,

(c) a wire screen arranged to continuously pass through said space between said openings for receiving said material to form said web,

(d) separator means adjacent said forming chamber for extracting a portion of the gas from a gas-fibrous material mixture passing therethrough and for delivering said fibrous material and the remaining gas to said forming chamber,

(e) first conduit means extending from said suction chamber to said separator means, said first conduit means including blower means for drawing a gas stream through said screen from said forming chamber to said suction chamber and recirculating a major portion of said gas stream through said conduit means from said suction chamber to said separator means,

(f) means for feeding fibrous material, without admitting air, into said first conduit means to be entrained by said recirculating gas stream to form said gas-fibrous material mixture,

(g) second branch conduit means extending from said separator means to said first conduit means at a point upstream of said fibrous material feed means for recycling said extracted gas from said separator means .to said recirculating gas from said suction chamber for supplying supplemental gas for entraining said fibrous material, and

(h) third branch conduit means extending from said second branch conduit means to a position adjacent said opening in said forming chamber for supplying additional gas to said forming chamber through the forming chamber opening,

(i) whereby the introduction of atmospheric air into the apparatus through said space between the forming chamber and suction box openings is reduced to a minimum.

6. The apparatus of claim 5 wherein said second branch conduit means comprises a pressure equalization chamber having an opening communicating with atmospheric air, said third branch conduit means communicating with said equalization chamber, whereby proper pressure distribution may be maintained in the apparatus.

7. The apparatus of claim 5 wherein said second branch conduit means comprises further separator means for removing any entrained fibrous material passing through said first separator means, said third branch conduit means being connected to said second branch conduit 8 means downstream of said further separator, whereby said third branch conduit means is free of fibrous material.

8. The apparatus of claim '5 wherein said second branch conduit means is connected to a source of gas having a low oxygen content to reduce the risk of fire.

9. The apparatus of claim 8 wherein said source of gas comprises an apparatus for dehydrating said fibrous material by means of hot flue gases.

References Cited UNITED STATES PATENTS 2,715,755 8/1955 Jones l9-156.3 2,940,134 6/1960 Heritage 19156.l 3,071,822 1/1963 Meiler l9156.3

DORSEY NEWTON, Primary Examiner 

